The signals elicited by activation of G protein coupled receptors have become increasingly complex. These receptors are now known to activate pathways associated with tyrosine kinase and cytokine receptors, although the mechanisms involved are not yet clear. Adrenergic receptors (ARs) affect growth and differentiation of many cells, often through activation of mitogen-activated protein (MAP) kinase pathways. We have shown that alpha/1A-AR transfected PC12 cells, norepinephrine activates three parallel MAP kinase pathways and causes differentiation into a neuronal phenotype similar to that caused by nerve growth factor. Preliminary data suggests that these responses do not involve known second messengers, and we now propose to use these cells to examine the complex signaling events initiated by alpha/1-AR activation. We will test the hypothesis that alpha/1-ARs activate signaling pathways in addition to Gq/11-mediated Ca/2+ mobilization and protein kinase C activation, that these responses may or may not involve heterotrimeric G proteins, and that they may be different for the three alpha-1AR subtypes: We will determine 1) whether human alpha/1a-, and alpha/1B and alpha/1D-ARs differentially activate second messenger, MAP kinase, and transcriptional responses in PC12 cells; 2) whether known second messenger pathways and/or G proteins are involved in MAPK responses; 3) whether alpha/1- AR subtypes activate Jak/Stat or other growth factor/cytokine signaling pathways; and 4) use alpha/1-AR activation of the three MAPK pathways to clarify their roles in growth, differentiation and apoptosis. These experiments will clarify mechanisms coupling AR activation to growth and differentiation, and provide important information on differences between closely-related subtypes.